The present invention relates to an indicator device which measures and makes a permanent record of the operational efficiency of a steam or gas sterilizer and in particular of the amount of residual air present in the sterilizer during a typical cycle of operation.
In steam sterilizing, it is well recognized that the ability to sterilize depends in large part on the adequate removal of air from the sterilizing chamber. For this reason a typical cycle involves the evacuation by one means or another of air prior to the admission of the sterilizing steam. Particularly when porous goods are being steam sterilized, any air in the goods acts as a barrier to the penetration of steam to the center of the goods and consequently, they will not be sterilized.
The usual method to insure that the sterilizer reduces air to an acceptable level is to periodically run a test cycle. The load utilized in the test cycle is a fairly standard test pack made up of porous goods such as linens and the like. Included in the pack is a spore strip which is incubated after the pack has been sterilized. If, after incubation the spore strip shows no bacteria growth, it is assumed that the sterilizer is operating properly. The drawback of such a test procedure is that the size of the test pack precludes the running of both the test load and an ordinary load at the same time so that while the test load is being run, the sterilizer is not available for normal use. Also, since the test load is run alone, there is no assurance that the sterilizer is operating properly between test loads.
There are devices available for continually monitoring the amount of air in the sterilizing chamber. Such devices typically monitor the environment within the sterilizing chamber by continuously bleeding a sample of the steam and entrapped air from the sterilizing chamber and analyzing this sample to determine its air content. Typical of such devices are illustrated in U.S. Pat. Nos. 3,402,991, 3,479,131 and 3,967,494. Such devices have the disadvantage of requiring special connections to the sterilizing chamber which themselves may become sources of air leaking into the sterilizing chamber when the chamber is evaluated.
The indicating device of the present invention requires no connection of exterior piping to the sterilizing chamber or a special test load. Instead, the indicator of the present invention may be placed into the sterilizing chamber along with the goods to be sterilized. The device requires a minimum of preparation and can provide a permanent record of each sterilizing cycle to show the amount of air, if any, in the chamber during the sterilizing cycle.
In sterilizing with a gas such as ethylene oxide, steam is often used to condition the goods prior to exposure to gas, the steam acting both to heat and moisturize the goods. Here residual air can also present problems so in another form, the present invention would have application to gas sterilizing cycles.